Google L4 || DSA Round 1 || Reject
- Experience
- 3 years
- Posted
- 20 Oct 2026
Summary
I interviewed for a Google L4 DSA round, tackled several graph‑based problems, and was rejected after the first round.
How it went
Education : Tier 1 CSE
YOE: 3
Current Company : MNC
cp stats:
lc ~2450 rated
cf ~1850 rated
Pasted Q at 5 mins:
Base Question - (10 mins)
Given a connected acyclic graph with every node having at most 3 neighbours, find a valid node which forms a binary tree.
Solved+coded+tc/sc discussion in 10 mins
Follow up 1 - (10 mins)
Now every node is either Black or White , at every depth in the tree colors should be alternating. Find a valid node.
Solved+coded+tc/sc discussion in 10 mins
Follow up 2 - (10 mins)
Now graph can be disconnected.
Clarified requirements and then
Solved+coded+tc/sc discussion in 10 mins
Follow up 3 - (10 mins)
Now every node is either Red , Black or White. Find a valid root node , only allowed sequence of depths is RWBRWB.... Root can be of any color.
Told brute force by selecting each node and doing bfs/dfs. He was not satisfied and asked me to optimize further.
3 mins gone.
Now barely 7 mins were left. I tried some parity or distance between same depth stuff but it didnt work, he didn't give any hints. For optimization I was trying to use dfs+parity to precompute some info but it wasn't helping much to identify a valid root.
Finally he said 45 mins over wasn't much satisfied, said bye bye and left.
After the Interview I segregated few cases and eventually derived an O(n) solution proving only 1 unique root is possible but its too late now :(
Bad experience, 10 mins for last follow up is not justified as it was pretty difficult. Also why did they ask 3 follow ups.
Interviewer wasn't communicating properly or even trying to help.
Got reject in this round, further rounds got cancelled.
Horrible experience , will never Interview with Google again.
They expect you to either know solution beforehand or solve it within 10 minutes.
Questions asked (4)
- 01
Find Root Forming Binary Tree in Connected Acyclic Graph
Data Structures & Algorithms
Given a connected acyclic graph where each node has at most three neighbours, identify a node that can serve as the root of a binary tree constructed from the graph.
- 02
Alternating Black/White Colors in Tree Depths
Data Structures & Algorithms
Building on the previous problem, each node is colored either Black or White. The colors must alternate at each depth level of the tree. Find a valid root node satisfying this color‑alternation constraint.
- 03
Root Selection in Possibly Disconnected Graph
Data Structures & Algorithms
Now the graph may be disconnected. Given the same degree constraints (≤3 neighbours per node), determine a valid root node that can form a binary tree for each connected component.
- 04
Root with Red/Black/White Sequence Constraint
Data Structures & Algorithms
Each node is colored Red, Black, or White. The allowed sequence of colors across depths is a repeating pattern like RWBRWB… (any rotation allowed). The root can be any color. Find a valid root node respecting this pattern.
How they prepared
I prepared by solving a large number of LeetCode problems (approximately 2450 rating) and practicing Codeforces contests (around 1850 rating), focusing on graph and tree algorithms.